1. Field of the Invention
The present invention relates to a method of decreasing the corrosion and wear of gun barrels. More particularly, the invention relates to a laminar additive which decomposes by the heat of firing to gaseous products which reduce wear and corrosion in gun barrels.
2. Description of the Prior Art
The effective life of gun barrels is dependent upon several factors of which two are basic or controlling factors. The first factor is the fatigue or deterioration of the mechanical properties of the metal of the gun barrel which is caused by thermal and stress cycling from repeated firing of the gun. The second factor, which is of importance, is the corrosion of the barrel which occurs upon repeated firing of the weapon which manifests itself in the form of bore enlargement or damage of the internal surface of the bore. In view of these detrimental problems there is active interest in the development of means for reducing the corrosion and fatigue problems in gun barrels caused by repeating firing of weapons.
In one prior art technique for reducing corrosion in gun barrels, the interior surfaces of the bore are coated or lined with a corrosion resistant material. In another approach a wear-reducing additive is incorporated within the propellants which forcibly expel a projectile from a gun barrel. The wear-reducing additive is normally structured as a sheath of material formed of an organic substance such as a polyurethane foam or paraffin frequently mixed with an inorganic material such as titanium dioxide. The sheath of material generally known as a laminar additive, is wrapped about the front end of the propellant charge behind the projectile (see FIG. 1). Although the exact reasons of how the sheath material functions as a corrosion reducing agent are not clearly understood, it is believed that the corrosion-reducing action arises from or is a function of the cellular structure (in the case of the polyurethane foam), or that combustion or vaporization of the sheath upon firing of a weapon forms a comparatively cool and/or unreactive layer of gas in close proximity to the barrel walls, or that a solid insulating layer is deposited on the surface of the bore.
Of the types of materials which are commonly used as additive sheaths are polyurethane foams which are extensively used in the United Kingdom, Canada and the United States, and a mixture of paraffin wax and titanium dioxide commonly known as "Swedish additive." It is also known that the substitution of talc for titanium dioxide gives rise to improved results. However, a problem with the conventional sheath materials is that after firing of a weapon, residues of the inorganic material remain on the interior surfaces of the barrel since the inorganic material is not volatile. This has possible unpredictable effects on the ballistic characteristics of the weapon because of the accumulated residue.
Another prior art procedure as described in U.S. Pat. No. 3,877,374 shows a method of applying a protective coating of a substance to the external surfaces of caseless ammunition. In the disclosed method the external surfaces of caseless propellant charges are coated with microcapsules of a vaporizable material such as wax, silicone oil, or the like encapsulated in a confining skin of gelatin, polyvinyl alcohol, epoxy, or the like. The coating of microcapsules performs the dual function of protecting the caseless propellant from the detrimental influence of heat because of the poor heat transfer characteristics of the encapsulated material, and of vaporizing by the heat generated when the propellent is fired which distributes the encapsulated material over the surface of the gun bore thereby protecting the surfaces of the bore from the corrosive effects of the combustion gases. This technique, however, is disadvantageous because of difficulties in manufacturing the microcapsules. The microcapsules also may not withstand rough handling, which could give rise to seepage of the encapsulated material into the propellant thereby having unpredictable effects on the ballistic characteristics of the weapon.
A need, therefore, continues to exist for a method of protecting the bores of gun barrels with a wear and corrosion resistant material in a manner which overcomes the deficiencies of the prior art methods.